Security nuts have as their objective to provide no convenient grip by means of which they can be removed. Removal can then be attained only by destruction or deformation. Thieves must work quickly, and means which require excessive time, or substantial tools to overcome a security feature will generally discourage a thief. Thus, it is not necessary that a security nut be absolutely non-removable, because often they later will need to be removed in order to replace or service the article they are protecting. Time-consuming inconvenience is generally sufficient.
Security nuts which are shaped so a wrench cannot get a grip on them, or which spin freely even if a grip can be attained, are known. For example, Gassaway U.S. Pat. No. 3,910,079 shows a bolt whose head is protected from access by an attached free-spinning cap which is also tapered so as to provide no gripping surface for a wrench. Access to the bolt can be attained only by removing a locked plug from the cap. The Gassaway device retains the capacity to engage the bolt with a tool, but shields the tool-engaging surfaces by means of a locked plug.
Such a device has the feature that tool-engaging surfaces do remain in existence, so that if the lock is overcome or released then the article can conveniently be removed. Of course in some installations this is considered to be an advantage, rather than a disadvantage.
A total absence of tool engaging surface will result in a less convenient but more secure device, because then a destruction or severe deformation of the fastener must always be accomplished, which takes time and strong tools. It is an object of this invention to provide such a device.